Ageing and spectroscopic properties of polyethylenes: comparison with metallocene polymer

The thermal and photooxidative stabilities of high, linear low and metalloc ene grade polyethylenes are compared using FTIR and hydroperoxide concentra tion analysis and thermal methods (DSC, TGA). The thermal ageing of solid f ilms follow the order LLDPE > metallocene > HDPE while for light stability the order is LLDPE > HDPE > Metallocene. Derivative UV and FTIR spectroscop ic analysis of the three polyethylene types show that the vinyl types and c oncentrations are different and that they reflect the thermal stability of the polymer materials. Hydroperoxide levels also appear to be important and correlate with the carbonyl index oxidation rates. Differences in catalyst residues play a less prominent role although the effect of the Ti levels m ay be important. The fluorescence and phosphorescence excitation and emissi on spectra of the three types of polyethylene are similar confirming earlie r identities on the role and presence of unsaturated carbonyl species. Ther e are however, significant differences in a long wavelength component in th e fluorescence emission indicating the presence of other active chromophore s. These were found to be significant in the case of the metallocene polyme r. These chromophores may contribute to the differences in the light stabil ity of the polymers with the metallocene exhibiting the greatest intensity and least stability followed by HDPE and LLDPE. (C) 1999 Elsevier Science L td. All rights reserved.